The proposed research is designed to provide quantitative data on the effects of exposure of the prenatal rat to ultrasonic energy. Exposures will be made to graded time-intensities of ultrasound after 9 or 15 days of gestation. Three types of frequency-pulse conditions, which are representative of pulse-echo, doppler, and diathermy techniques will be used. Detailed characterization of the ultrasonic beams will be made, as well as attempts to estimate the energy absorbed by the conceptus. The animals exposed at the earlier time will be sacrificed at 20 days of gestation, prenatal mortality noted, and the fetuses examined in detail for the presence of malformation. Those exposed at the later time will be allowed to deliver and the incidence of mortality and gross anomalies of the offspring determined. The growth and development of the offspring will be studied with particular emphasis on neurological, behavioral, or reproductive deficits. The incident and absorbed energies associated with various clinical procedures will be estimated. These values will be compared with the "dose-effect" relationships obtained in these experiments for an analysis of the safety and/or hazard associated with current clinical techniques.